Excess Exercise Tied To Osteoporosis, Disrupted Menstruation

August 07, 1986|By Dr. Jean Mayer and Jeanne Goldberg, R.D.

If it seems to you that women are becoming more physically active, you`re right. The motivation to begin an exercise program ranges from maintaining peak health, to losing weight, to competing in a marathon.

The importance of keeping physically fit is beyond debate. Unfortunately, physical activity, especially when combined with weight loss, can affect menstrual cycle, either by delaying the onset of puberty or, after puberty, by disrupting normal menstruation.

Among competitive sportswomen, delayed puberty is a common problem. And loss of menstruation--amenorrhea--occurs in up to 50 percent of competitive runners and ballet dancers, 25 percent of noncompetitive joggers and 12 percent of swimmers and cyclists. By comparison, amenorrhea affects only 3 to 5 percent of women in the general population.

Previously, amenorrhea had been considered a benign side effect of endurance training. Now it appears that in young women it may be accompanied by heightened risk of osteoporosis, the increased bone porosity that strikes 15 million to 20 million elderly in the United States.

Dr. Christopher Cann, of the University of California at San Francisco, first reported a link between exercise-related amenorrhea and bone health in 1982. Dr. Cann measured spinal bone density in 25 amenorrheic women, including six athletes. As a group, the amenorrheics had lower bone densities than women with normal menstrual cycles.

To date, six studies of young women with amenorrhea have reached the same conclusion.

Several also have shown an increased incidence of stress fractures and curvature of the spine in women who experience either delayed onset of puberty or prolonged amenorrhea. This observation came as a surprise, since it long had been believed that exercise increased bone density.

What causes this disruption? The female hormone, estrogen, promotes calcium retention in bone. When women undergo menopause, estrogen levels drop dramatically. This is viewed as a major explanation for accelerated bone loss at that time.

Similarly, the hallmark of amenorrhea in young women is low estrogen levels. And the low estrogen levels in women who develop amenorrhea may account partially for their lower bone densities.

Three recent studies of women athletes with amenorrhea paint a more complicated picture. It has been shown that amenorrheic athletes tend to eat fewer calories than menstruating athletes. The most recent study was one that confirmed earlier observations of lower spinal density in amenorrheic women than in normally menstruating women.

A group of researchers led by Miriam Nelson and Elizabeth Fisher, of the Tufts University Human Nutrition Research Center on Aging, found that those in the amenorrheic group consumed an average of 500 calories less than menstruating women.

Since both groups ran the same number of miles a week and maintained the same degree of body fat, this finding was puzzling. Among the possible explanations:

The amenorrheic group systematically may have underreported food intake, and that could indicate an eating disorder.

They may reduce energy expenditure radically in nontraining activities, including more sleep and rest time.

Or they may experience increased efficiency of nutrient utilization to preserve body mass.

Which if any of these hypotheses is correct remains to be explored.

In the past it had been thought that a low percentage of body fat predisposed a woman athlete to amenorrhea.

But the three studies that explored diet and bone health in amenorrheic and normally menstruating women athletes revealed no difference in percentage of body fat. Indeed, even some obese women who have lost a lot of weight but are not yet thin experience amenorrhea.

Thus weight loss itself may be more important than the absolute percentage of body fat.

It is possible that restricted caloric intake predisposes the athlete to amenorrhea.

Dr. Beverly Bullen, at Boston University, compared the effects of started a running program while maintaining weight, with starting a similar exercise program while losing weight. Her results, published in the New England Journal of Medicine, indicated that women who lost weight when they started the exercise program were more likely to have menstrual disturbances than those who maintained their weight.

The results of these studies show that delayed puberty or amenorrhea in young women should not be viewed as a simple side effect of exercise but as a warning signal that estrogen levels have dropped too low and that bone health is threatened.

They do not suggest that women should give up exercise.

Rather, a woman experiencing changes in her menstrual pattern should (1)

consult her gynecologist, (2) take a clear-sighted look at her eating habits and weight change and (3) consider seeking the guidance of a registered dietitian who can help set her diet on the right track to promote bone health. -- -- --

Q--Is there any nutritional difference between the various sweeteners--in particular, white sugar, brown sugar and honey?